In a homing torpedo of the type which transmits a pulse and receives a return or "echo" pulse, such as the "Underwater Target Detection System" disclosed in the copending patent application of Jack H. Slaton, filed Jun. 18, 1962, Ser. No. 203,406, it is desirable to obtain high sensitivity and simultaneously maintain a low false alarm rate.
Ideally, a homing torpedo should be capable of attacking "real" targets without being influenced by signals from undesired targets or from the ocean itself. However, since water is such a poor medium for transmission, it has often been the practice to home on any acoustical signal received.
Torpedo countermeasures, therefore, seek to confuse the homing system of a torpedo by generating acoustic signals of their own which resemble target echoes or target-radiated noise. In some systems it has been the practice to use signal processing techniques in an attempt to ignore the signals produced by the countermeasures. This practice results in ignoring certain target signals as well, and therefore causing reduced effectiveness of the homing system. Furthermore, this practice ignores the fact that countermeasures are normally in the vicinity of the "real" target, and to be convenient, must be smaller in size than the "real" target.